#include<iostream>
#include<cmath>

int main()
{
	using namespace std;
	double solut(double, double, double, double);
	double a, b, c, d;
	
	cout << "input a,b,c,d";
	cin >> a >> b >> c >> d;
	cout << solut(a, b, c, d) << endl;
	return 0;


}
